ArcGIS get vertex position on touch move

I'm using ArcGIS runtime 100.12.0 with Xamarin forms and I'm trying to show distances between vertexes. I did it with the event GeometryChanged, but now I need to show the distances when the touch moving event occurs, it seems like there aren't any events or commands to get the MapPoint position when Vertex is moving, then I get touch moving event like this:

<Grid Grid.Row="0">
            <esriUI:MapView
                x:Name="MainMapView"
                GraphicsOverlays="{Binding GraphicsOverlays}"
                Map="{Binding Map}" />
            <Grid.Effects>
                <local:TouchEffect Capture="True" TouchAction="OnTouchEffectAction" />
            </Grid.Effects>
</Grid>

But when I get the selected vertex, the position is the same when touch moving occurs, I tried to extend the SketchEditor to customize events, but an error occurs "Cannot derive from sealed type 'SketchEditor'.

Can you please give me some ideas, advice, or solutions, thank you!